1. Field of the Invention
The present invention relates to an electromagnetic lens shutter apparatus for a camera. More particularly, this invention relates to a camera having an electromagnetic lens shutter apparatus for a camera which can be actuated on an aperture-priority basis.
2. Description of the Prior Art
Generally, the opening and closing functions of a lens shutter blade are carried out by controlling a direction and a time of an electrical current which flows through an electromagnet in a camera having an electromagnetic lens shutter apparatus. Such an electromagnetic lens shutter apparatus has a simple construction compared with a mechanical shutter which uses a mechanical spring force to effect the opening and closing functions of a lens shutter blade.
U.S. Pat. No. 4,881,093 discloses an electromagnetically operated lens shutter assembly for a camera which includes permanent magnets which are affixed to lens shutter blades. An electromagnetic field is generated by a number of armatures which interact with the permanent magnets to cause the lens shutter blades to move between open and closed positions. The configurations of the permanent magnets and armatures permit the blades to be held in the open and closed positions without the further application of current to the armatures. Also, the permanent magnets are levitated by the electromagnetic field in order to facilitate movement of the lens shutter blades between the opening and closing positions. However, such a lens shutter cannot be applied to an automatic focus and exposure camera.
Japanese Patent Publication No. 90-33130 describes an electromagnetically operated lens shutter mechanism in which a first moving coil member for moving a lens shutter blade between an affixed permanent magnet and a yoke at an opposing position of the permanent magnet and a second moving coil member for deciding an open degree of the lens shutter blade are provided. An operation of both moving coil members is carried out at a predetermined time difference, so that an automatic exposure is effected. However, since the lens shutter in this manner does not have an automatic focusing function, it is applied only to a simple fixed focus camera and cannot be applied to a zoom camera commonly used at the present time.
The inventors of the present invention made a Korean Pat. Appln. No. 92-21057 which describes an electromagnetic lens shutter apparatus which has a compact construction and can be applied to an automatic focus and exposure control camera. However, focusing and exposing is automatically controlled in accordance with a program previously inputted in a central process unit.
In some instances, in addition to an automatic focus and exposure control function there is a time when a user may wish to adjust an F number manually, namely the lens shutter has to be operated on an aperture-priority basis. For example, this function is required in case that the user wants to adjust a depth of field. In this case, in addition to an automatic exposing adjustment function, a lens shutter apparatus having a semiautomatic function is required in order to permit a lens shutter speed to be adjusted in accordance with the F number which is set manually in advance.